Fory the Mobylettes out there (I don't theink the original poster was doing timing on a Moby)...
OK, if the rubbing block (the part of the points that rides on the cam) wears down, all it will do is reduce the point gap. If you open the points to the maximum and reset them to the proper gap you have compensated for that wear.
A few weeks ago I used a ruler and an ohmeter to set the timing as accurately as possible. A couple things I can tell you - the points are actually opening before it is apparent to the eye. If you're setting them to where it looks like they're just opening you're probably too late.
My little testing also showed that the quick method really does work, and you can set the timing in under five minutes easily (assuming you can get the cam off - a puller helps!)
Take out the spark plug and use something (like na allen wrench) to indicate when you are at TDC. Slip the cam on with the riser toward the top and the holes pointing towards about 10:30 or 11 o'clock. While holding the crank at TDC, rotate the cam towards about one o'clock (which should be opening the points) and line up the holes on the cam with the axis of the cylinder, or just slightly to the left.
In the picture below you can see how the holes relate to the cylinder axis at TDC, and this is with the timing set to 2mm TDC very accurately. Setting to 1.5mm would put it even more in line with the axis. So yes, the "quick and dirty" method of putting the piston at TDC and aligning the cam up this way really does work!